This study reviews changes and differences in perinatal mortality for similar populations over a period of rapid change in technology, use of cesarean sections, and medical management of high risk pregnancies. It will explore whether high rates of neonatal mortality in certain cities reflect phenomena other than shifts in mortality from the late fetal period and to track differences in perinatal experience among biologically similar populations. The approach will be a secondary analysis of data sets provided by the National Center for Health Statistics based on 100 percent reporting of perinatal deaths. Categorical screens of both twenty and twenty-eight weeks gestation to deaths through seven days and one month will be used to eliminate reporting differences among cities and shifting of neonatal deaths into the latter period. These data have not been available publicly for analysis. The analysis should provide new baseline information on the true outcome of pregnancies in biologically similar populations.